How should I stage and initiate treatment for a dog presenting with congestive heart failure?

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Canine congestive heart failure (CHF) is staged using the ACVIM classification system, and stage C (symptomatic) disease is treated with quadruple therapy: furosemide or torsemide, pimobendan, spironolactone, and enalapril or benazepril. 1 Staging drives treatment decisions. Stage B1 describes preclinical disease without cardiac remodeling, and stage B2 describes preclinical disease with echocardiographic evidence of remodeling — both are asymptomatic. Stage C is symptomatic CHF responsive to standard therapy, and stage D is refractory CHF despite standard therapy. 8 Dogs with stage D disease are distinguished in part by serum chloride below 103.5 mmol/L, which accurately identifies this refractory population. 5 For acute decompensated CHF, furosemide is administered at 2 mg/kg IV at presentation, followed by oral furosemide at 2.3 mg/kg PO q12h 4.6 mg/kg/day total for ongoing management. 3 When furosemide becomes insufficient at higher doses in refractory (stage D) disease, earlier transition to torsemide is warranted, as furosemide oral bioavailability does not correlate reliably with serum concentration at higher doses. 5 Chronic stage C management combines four drug classes. Spironolactone is initiated at 1.5 mg/kg PO q12h 3 mg/kg/day total, and enalapril at 0.4 mg/kg PO q12h 0.8 mg/kg/day total. 3 Pimobendan is included as the inodilator component of quadruple therapy. 1 Inhibition of the renin-angiotensin-aldosterone system (RAAS) with ACE inhibitors and spironolactone improves potassium retention and increases beneficial RAAS metabolites in stage C and D dogs. 5 Dietary sodium restriction is recommended alongside pharmacologic therapy. A low-sodium diet with balanced protein, phosphorus, and antioxidants is appropriate for stage C dogs. 3 High-sodium food and treats should be avoided. 3 Fluid therapy is approached with caution in CHF patients. When IV fluids are necessary, 0.45% NaCl with 2.5% dextrose administered at half to daily maintenance rates is the re